JPH04318841A - High chloride iodine silver halide emulsion containing iodine at high rate - Google Patents

Abstract

PURPOSE: To maintain advantages in the case the emulsion contains chlorine ions and further to improve sensitivity by incorporating the cubic crystal grain structure of high-chloride silver iodohalide with a high ratio of iodide into the emulsion. CONSTITUTION: This emulsion contains the high chloride iodine silver halide grain structure having the ratios of chlorine ions, bromide ions and iodide ions within the boundary enclosed by A to D of Fig. Namely, the upper limit of the iodide is regulated and the level to take in the max. iodide in the silver iodohalide emulsion prepared for comparison is 12.8mol%, based on the total silver. This level exists on a I-Cl axial line slightly below the point A where the iodide level of 13mol% exists. The level to take in the max. iodide by the silver iodohalide emulsion contg. the bromide ions and iodide ions of equiv. mol amt. is 27.3mol%, based on the total silver. This level exists slightly below the point B of 28%. Namely, the axial line B-A exists slightly above the upper limit iodide concn. in the conventional high-chloride silver iodohalide grain structure.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to silver halide photography. More specifically, this invention relates to new silver halide emulsions for use in photography.

0002

BACKGROUND OF THE INVENTION Photographic silver halide emulsions commonly contain radiation-sensitive microcrystals called grains. Radiation-sensitive grains containing essentially silver iodide, silver bromide or silver chloride in the absence of other halides are respectively known. Radiation-sensitive particles containing mixtures of halides in their crystal structure are also known. However, since silver iodide tends to provide a crystallinity different from that of silver bromide or silver chloride, the range of combinations of halides that can be present in the crystal structure is limited.

For a range of possible combinations of iodide, bromide and chloride compared to silver halide crystal structures that can be achieved, see FIG. 1 (a matrix containing the proportions of all three halides). This is the easiest way to imagine it. First of all, considering only the extreme points, the total halides are I 100%, Br1
00% and Cl 100% points are occupied by the indicated halides. Total halides are Cl-Br
The 0% axis is occupied by iodide. The total halide is dominated by bromide on the I-Cl 0% axis. Total halides are Br-I
The 0% axis is dominated by chloride. At all other intermediate positions in the matrix a mixture of chloride, bromide and iodide is present, and the concentration of each halide at any intermediate point chosen is equal to that of the 100% point of the matrix and its halide. is determined by the distance from the 0% axis to the midpoint.

Silver chloride and silver bromide each form a face-centered cubic rock-salt crystal lattice structure. These crystal structures are composed of silver ions and (a) bromide ions as the sole halogen ions, (b) chloride ions as the sole halogen ions, or (c) mixtures of chloride and bromide ions in all proportions. It is known that Therefore, Figure 1
All possible combinations on the Br-Cl axis of are known in silver halide grain structures. Their crystal structures differ only in their unit cell dimension (reflecting the difference in size of chloride and bromide ions). The measured value of the crystal lattice parameter can be obtained by the current method of measuring the halide ratio.

Silver iodide exhibits a face-centered cubic halite crystal structure only at very high pressure levels (3,000-4,000 times atmospheric pressure). This form of silver iodide, called σ-phase silver iodide, shows no relevance to silver halide photography. The crystal structure of silver iodide, which is stable under ambient conditions, is hexagonal wurtzite, commonly referred to as beta-phase silver iodide. Another crystal structure of silver iodide that is stable enough to be used at room temperature is the face-centered cubic zinc blende type, commonly referred to as gamma-phase silver iodide. Silver iodide emulsions containing both a β-phase crystal structure and a γ-phase crystal structure have been prepared. The fourth crystalline form of silver iodide is
The Theory of Photography by James
ic Process, 4th edition, Macmillan (
1977), page 1, and its formation at a temperature of 1
It has a body-centered cubic crystal structure that requires a temperature of 46°C. (James, pages 1-5, are relevant to that and the following parts of this discussion.)

When considering mixtures of bromide and/or chloride ions with iodide ions in the crystal structure of silver halide grains, there are two possible conditions to consider. That is, (1) how many bromide and/or chloride ions can be tolerated in the silver iodide crystal structure, and (2) how many iodide ions can be allowed in the silver bromide and/or silver chloride crystal structure. Is it acceptable?
It is. Emulsions satisfying (1) are commonly referred to as "high iodide" silver halide emulsions, and their iodide content is generally at least 90 mole percent, based on total silver. It is said. U.S. Pat. No. 4,184,878 to Maternaghan illustrates high iodide silver halide emulsions. Because silver iodide emulsions are known to have limited photographic utility, research into variants containing bromide and/or chloride ions has been limited. Moreover, before bromide and chloride ions partition themselves into separate phases, the silver iodide crystal structure generally cannot tolerate the incorporation of more than 10 mole percent bromide and/or chloride ions. It was believed that he was deaf. Referring to FIG. 1, a high iodide silver halide crystal structure exists within the region identified by points W, V and I.

Emulsions containing an overwhelming majority of iodides satisfy condition (2). The most widely used photographic emulsion is the silver iodobromide emulsion. All references to complex halide emulsions, grains and crystal structures follow the nomenclature convention for their concentrated halides (see page 4 of the James reference cited above).

The silver bromide crystal structure can be less forgiving than that of an equivalent amount of iodide. The maximum amount of iodide incorporated into silver bromide was determined by H. Hirsch.
rsch) by “Photographic Em
ulsion grains with cores
: Part I. Evidence for th
e Presence of Cores"J. of
Photog. Science, Volume 10 (19
62), pp. 129-1344
It is 6.5 mol%.

Since chloride ions are considerably smaller than bromide ions, the size difference between chloride and iodine ions is much larger than that between bromide and iodine ions. Therefore, it stands to reason that iodine ions may be less tolerated in the silver chloride crystal structure than in the silver bromide crystal structure. Silver iodochloride emulsions are known. Studies have shown that the upper limit for iodine incorporated into the silver chloride crystal structure is 13 mole percent, based on total silver, following conventional emulsion preparation methods (as shown in the example below). Referring to Figure 1, the limits of iodide in a conventional silver iodochloride emulsion along the axis I-Cl are the Cl point (I 0 mol%) and the A point (I 13 mol%).
Identified by

By selecting each halogen ion,
It is known to confer certain photographic advantages. Although known and used for many years for selected photographic applications, the rapid development and ecological benefits of high chloride silver iodohalide emulsions have led to the use of these emulsions in a broader range of photographic applications. It has continued to inspire me to do so. As used herein, the term "high chloride silver iodohalide" refers to emulsions, grains and crystal structures in which the concentration of halogen ions other than iodide ions is in excess of the iodide ion concentration or It is defined as satisfying the conditions that the concentration of chloride ions is at least equal to the concentration of bromide ions, and that the concentration of chloride ions is in excess or at least equivalent to the concentration of bromide ions. High chloride iodohalides include silver iodochloride, silver iodochlorobromide and silver bromoiodochloride. Referring to FIG. 1, all of the silver halide compositions within the area bounded by points Cl, Y, C and D satisfy the definition of high chloride silver iodohalide.

When considering the possibility of substituting chlorine ion as the halide chosen in place of bromide ion in silver halide photography, the problem of iodine incorporation arises. The vast majority of photographic emulsions contain iodide for the purpose of improving their photographic properties. Conventional high chloride iodohalide grain structures are limited to acceptable compositions within the region defined by points Cl, Y, B and A in FIG. The iodide concentration in the oxides is limited to a maximum level that is well below the maximum level acceptable in the silver iodobromide and silver iodochlorobromide grain structures. The iodide concentration of high chloride iohalide emulsions is
Specifically, the bromide ion concentration is limited to less than 20 mol%. In some high-volume photographic applications for silver iodobromide emulsions, where the grains contain high iodine levels for the purpose of improving the speed-granularity relationship or increasing interlayer effects, there are It is not possible to replace bromide ions with chloride ions because high chloride iohalide emulsions are not available that can tolerate corresponding levels of iodide ions.

Although the comparative example below shows a maximum iodide concentration in silver chloroiodide based on total silver of 13 mol % iodide concentration, numerous published studies on silver halide interfaces have consistently found that Suggests that it is limited to lower iodide. The following teachings are considered representative.

[0013] H. Chateau
, Comptes Rendus Academy
Des Sciences Paris, 249, 1
959, pages 1887-1889 (the iodide content of silver chloroiodide was found to be 9.3% compared to the expected value of 7.5%).

[0014]K. Cornwell
l) and R.W.D.
yson), “Thermoelectric Pro
Parties of the Molten Sil
verChloride-Silver Iodide
"Eutectic Mixture", Brit.J
．． Appl. Phys. (J.Phys.D), 19
69, ser. 2, vol 2, pages 305-307 (provides a phase diagram showing silver iodide concentrations in silver chloride up to about 10 mole %).

[0015] V.V. Groznetsky (V.V.
．． Groznetskii), V. D. Zhuraviev, G. A. Kitaev and L. V. Zhukova (
L. V. Zhukova), “Thermal And
ysis of the Agcl-AgI and
AgBr-AgI Systems”,Russian
Journal of Inorganic Che
mistry, vol. 33 (3), 1988, 39
Pages 9 and 400 (report a phase diagram similar to that of Cornwell et al., but the silver iodide concentration in silver chloride suggests an even lower limit).

[0016]

OBJECTS OF THE INVENTION It is an object of this invention to obtain a compound in which the chloride ratio is equal to or greater than the bromide level, and so that the iodide level is achievable by conventional emulsion preparation methods. It is an object of the present invention to provide useful photographic emulsions containing increased levels of cubic lattice grain structure.

[0017]

[Means for Solving the Problems] One aspect of the present invention is
A photographic silver halide emulsion comprising a high chloride silver halide grain structure in which chloride, bromide and iodide ions are selected to be within the boundaries marked A, B, C and D in FIG. directed towards.

The BA axis of FIG. 1 defines the upper limit of iodide that can be incorporated into high chloride silver iohalide crystal structures prepared by conventional photographic emulsion preparation methods. These limitations were confirmed by the emulsion preparations included in the examples below for comparison purposes. The highest iodide incorporation level achieved in a silver iodochloride emulsion prepared for comparison purposes was 12.8 mole percent, based on total silver (see Example 1). This silver iodochloride composition is located on the I-Cl axis just below point A in FIG. 1, where there is an iodide level of 13 mole percent. The highest iodide uptake level achieved with a silver iodohalide emulsion containing equimolar amounts of chloride and bromide ions prepared for comparison purposes was 27.5%, based on total silver.
3 mole % (see Example 4). This composition is
In Figure 1, point B has an iodide level of 28 mol%.
located slightly below. Axis B-A lies just above the upper iodide concentration limit in conventional high chloride silver iodohalide grain structures.

The present invention provides a high chloride silver iohalide grain structure in which the proportions of chloride, bromide and iodine ions are chosen to lie within the boundaries bounded by A, B, C and D in FIG. A photographic silver halide emulsion comprising: That is, the high chloride silver iodohalide grain structures provided by this invention contain concentrations of iodide that exceed the maximum iodide uptake levels of conventional high chloride iodohalide emulsion grain structures. In one preferred embodiment, where iodide levels are further differentiated from conventional grain structures, the high chloride iohalide grain structures reside within the boundaries bounded by A', B', C, and D in FIG. Indicates the ratio of chloride, bromide and iodide ions, where A' and B' require an iodide concentration 1 mol% (preferably 2 mol%) higher than A and B, respectively.

The discovery of increasing iodide concentrations in high chloride iohalide grain structures suggests that under normal emulsion preparation conditions the limit of iodide incorporated reaches the saturation limit of iodide in the face-centered cubic lattice. This was made based on the assumption that this is the result of Next, (1) conditions are found that increase the iodide saturation limit, and (2) excess iodide incorporated under these conditions returns to the emulsion as produced at ambient conditions of processing and use. By doing so, it was provided that the iodide concentration can be increased when the face-centered cubic structure does not separate. Of course, until conditions satisfying the preparation of emulsions are devised and demonstrated, whether condition (2) is satisfied remains entirely speculative.

When considering how higher silver iodide saturation levels can be created in face-centered cubic structures, it is common to run the aqueous silver salt into an aqueous dispersion medium containing an organic hydrophilic colloid peptizer. The problem was to prepare photographic silver iohalide emulsions by. Since the silver iodohalide formed through precipitation must remain dispersed, precipitation must be limited to temperatures suitable to maintain the medium in a dispersed liquid phase. To gradually increase the vapor pressure of water by heating, a temperature of 90°C represents an accepted practical upper limit for the preparation of silver halide emulsions in a well-controlled and reproducible manner. Although the emulsion preparation temperature can be increased to 100° C. (the boiling point of water), estimates of iodide levels from working temperatures did not show a significant increase in iodide levels.

[0022] Therefore, a completely different preparation process from the conventional photographic emulsion preparation method was devised. It has been proposed to use a combination of emulsion preparation temperatures in excess of 130°C and high pressures. It was assumed that high pressure alone was ineffective, and that it could not be achieved without the above-mentioned high temperature and high pressure.

When preparing a silver iodohalide emulsion, 13
As an operation to achieve a temperature exceeding 0°C, (a)
It has been devised to prepare separately a high chloride silver halide emulsion containing no iodine and (b) a silver iodide emulsion with an average size of less than 0.05 μm. Emulsions (a) and (b) are then blended and subjected to a pressure chosen so that the blended emulsion is heated to above 130°C without boiling, and to contain high iodide levels. Ostwald growth was carried out under conditions that resulted in high chloride silver iodohalide grains formed. In another method of preparation, all of the halides can be precipitated simultaneously to provide a silver halide mixture phase. When this blending step was omitted and heating and pressurization were performed, results similar to those described above were achieved. It is particularly preferred to apply heat and pressure to the emulsion while it is being transported. The emulsions of this invention are therefore suitable for continuous preparation methods.

For the purpose of demonstrating the feasibility of the above preparation method to increase the iodide content of the silver iodochloride emulsion shown in E2 of FIG. (Example 2 below)
). This represented a 10% increase over the control iodochloride emulsion located just below point A on the I-Cl axis in Figure 1 (Example 1 below). In other words, the iodide concentration in the silver iodochloride emulsion increased by 77% from point A. At equimolar concentrations of bromide and chloride ions, the level of iodide uptake increased from 27.3 mol% to 39.6 mol% based on silver, as shown at point E6 in Figure 1 (see Example 6 below). ). This was a 45% increased iodide concentration.

High chloride silver iodohalides satisfying the requirements of this invention are those in which the incorporation of silver iodide into the high chloride face-centered cubic lattice grain structure takes place under conditions of high temperature and pressure. This is considered to be evidence that can be strengthened by Various studies conducted to date indicate that the above-mentioned attempts to achieve high chloride iohalide emulsions with high iodide contents are viable, but they show no signs of having an upper iodide uptake limit. There wasn't. To this end, the studies reported have been aimed at demonstrating the feasibility of the preparation methods rather than optimizing them. The preparation method was chosen as the simplest and most useful approach to achieve particle growth under high temperature and pressure. The method of preparation of this invention from soluble halides and silver salts (similar to operations used in batch single jet precipitation and batch or continuous double jet precipitation)
If silver halide were modified to form in situ, the incorporation of silver iodide into a rock salt type face-centered cubic lattice host would be increased. In particular, increasing the precipitation temperature and choosing a peptizer to increase thermal stability can
Other parameters that can increase iodide uptake levels are considered.

Apart from the features specifically described as essential to the practice of this invention, the high chloride iohalide emulsions and methods of their preparation are also suitable for conventional emulsions and methods of their preparation. Research Dis
closure, Vol. 308, 1989 1
February, Item 308, 119, especially Section I (
Attention is drawn to Emulsion Preparation and Formats), and Section IX (Vehicles and Vehicle Extending Agents). Research
Disclosure by Kenneth Mason
Publications, Ltd. (Dudley
Annex, 21a North Street,
Emsworth, Hampshire PO10
7DQ, England).

In the simplest embodiment of this invention, the novel grain structure of this invention is found in a majority, if not every grain of the emulsion, and is spread substantially uniformly throughout each grain. However, the new particle structure also
It is also possible to form only part of the particle. For example, the novel particle structure may form only the particle core or only the particle shell. Additionally, it is understood that it is common to mix emulsions of various grain populations to match emulsions to particular photographic populations.

[0028]

[Examples] This invention will be better understood by referring to the following specific examples. All X-ray powder diffraction patterns for each emulsion were performed using CU KB radiation. Silicon powder was added to the emulsion sample so that the 2θ value could be corrected with an internal standard.

For a given binary silver halide phase at room temperature (25° C.), the cubic lattice constant "a" required to determine the halide composition from X-ray diffraction data using the following equation: can be calculated.

a(BrCl)=5.5502+0.002246[B
r] a (ICl) = 5.5502 + 0.00635 [I] a
(IBr)=5.7748+0.00363[I]

0
[Br] and [I] are each mol%
Bromide and iodide concentrations are shown. These equations are given in James, cited above, page 4. From these equations the following equation for the ternary silver halide phase was derived.

[0032]

[Math 1]

In the above formula, a(IBrCl) is the lattice constant of the AgIBrCl phase at room temperature, and a(Br
Cl) is Ag with the same Br to Cl ratio as the AgIBrCl phase.
Although it is a lattice constant of the BrCl phase, it does not contain an iodide component.

Example 1 (FIG. 1, below point A) This example is a control. 12. AgICl emulsion grains precipitated at 90°C.
It is illustrated that only 8 mol% iodide was incorporated.

7.5% bone gelatin and 0.1M at 90°C
Into a stirred reaction vessel containing 400 mL of NaCl solution, 2.
5M AgNo3 solution at 1 mL/min, and 2.025M NaCl and 0.575M Na
Solution I was added at the rate necessary to maintain a pAg of 6.6. After 5 minutes, increase the silver addition rate to 5.3 mL/m in 30 minutes.
accelerated linearly to in. Total silver consumed is 0.
It was 25 moles.

If a single homogeneous phase were formed, it would be AgICl containing 23 mole % iodide. The X-ray powder diffraction pattern of the final emulsion showing reflections of AgICl{420} is centered at 2r = 67.12° and has dissolved iodide 12 as calculated from the equation provided above for a(ICl). It was .8%. Furthermore, free A
Diffraction due to gI was also observed.

Examples 2 and 3 These two examples demonstrate that dissolved iodide levels in AgICl emulsion grains can be significantly increased by forming them at elevated temperatures. A level of 22 mole % was achieved.

Example 2 (Figure 1, point E2) 150 mL of 4MAgNO3 solution was added to a stirred reaction vessel containing 4 L of 5% bone gelatin solution at 35° C. and pH 5.6.
/min and 4M NaCl solution to pAg 7.8
was added at the rate necessary to maintain the Precipitation was stopped after adding 4 mol of AgNO3. Next, pAg
was adjusted to 8.1 with NaCl.

A portion of this emulsion was mixed with a fine-grained AgI emulsion as shown in Table I below (AgI emulsion has pAg
10.3 and consisting of particles <0.05 μm). The mixture was placed in an autoclave and heated to 689.5 under nitrogen atmosphere.
The pressure was increased to kPa (100 psi). Next, these were cooled to 40° C. over 3 minutes. The resulting emulsion was washed to remove NaNO3 and resuspended in 5% gelatin solution.

An X-ray powder diffraction pattern was taken. For each emulsion, A from the position of AgICl{420} reflection peak
g The percentage of dissolved iodide in the Cl lattice is expressed as above a
Calculated using the equation for (ICl).

[0041]

[Table 1]

As the amount of iodide added increases,
Note that the peak position of the {420} reflection shifted in response to a level of 22.1 mol % iodide dissolved in the AgICl particles. The X-ray powder diffraction pattern of Emulsion B is shown in FIG. 2, where 2θ is the scattering angle and the highest scattering density was identified with a value normalized to 100. Peaks 1 and 4 were generated by the silicon internal standard. Peak 2 is the {331} reflection and peak 3 is the {420} reflection. This emulsion consisted of grains having an average diameter of 0.5 μm.

Example 3 A fine grain AgCl emulsion was prepared as in Example 2 except that the emulsion was precipitated at 40° C. using 4 L of 10% bone gelatin solution to give a pAg of 7.5.

[0044] AgICl emulsion is composed of AgCl emulsion and AgI
Prepared as in Example 2B except that the emulsion mixture was heated to 150°C and held at this temperature for 5.0 minutes. The emulsion was cooled to 40° C. (required 3 minutes), and H. Yutzy and F. Rus.
The phthalated gelatin coagulation method of U.S. Pat.

The resulting emulsion, consisting of 95% of the grains having an average size of 0.30 μm, was within the size range 0.19 μm to 0.41 μm. A scanning electron micrograph of this emulsion is shown in FIG. The X-ray powder diffraction pattern of this emulsion shows an AgICl{420} reflection peak,
It was centered at 2θ=66.43°C. This peak position indicates that the particles have 21 mol% of iodide dissolved in the AgCl lattice.
Indicates that it contains

Example 4 (FIG. 1, bottom of point B) This example is a control. It is shown that up to 27.3 mol% iodide can be incorporated into the 1:1 AgClBr phase precipitated at 90°C.

A stirred reaction vessel containing 400 g of 7.5 wt% bone gelatin prepared in 0.1 M chloride with NaCl was injected with AgNO3 solution (2.0 mL/min) at 2.0 mL/min.
5M) and then halogen ion salt solution at 2.0
It was added at mL/min. The composition of this halogen ion solution is shown in Table II below. Note that the NaCl compound is present in excess in an amount necessary to maintain a constant 0.1 M chloride ion excess in the reaction vessel. The silver solution and halide solution consumed are the same, totaling 0.2
5 moles of silver were added.

[0048]

[Table 2]

X-ray powder diffraction analysis showed that emulsion 4B contained two phases. One phase containing mixed halides was the composition in which a single phase was observed in Emulsion 4A. The other phase consists essentially of silver iodide. This analysis showed that the iodide concentration in the mixed halide phase could not be increased by increasing the proportion of iodide present in the precipitate.

EXAMPLE 5 This example consists of phase 1I having a composition of 35.6 mol % I, 32.2 mol % Br and 32.3 mol % Cl.
g A method for preparing a BrCl emulsion is shown.

Fine particles containing a predetermined amount of chloride, bromide and iodide, but consisting of multiple phases, were prepared by the following procedure. 10% in 0.028M NaCl at 40°C
In a stirred reaction vessel containing 4 L of bone gelatin solution, add 4M A
gNO3 solution at 150 mL/min, and 1.
33M NaCl, 1.30M NaBr and 1
．． A 40M NaI solution was added at the rate necessary to maintain a pAg of 7.5. The total silver solution and halide solution consumed was 1.00L.

A part of this fine grain emulsion was placed in an autoclave and heated to 689.5 kPa (100
psi). Heat to 160°C with stirring, hold at this temperature for 5 minutes, then increase to 40°C over 3 minutes.
Cooled to .

The obtained particles were composed of particles having an average diameter of 0.8 μm. The X-ray powder diffraction pattern of this emulsion is AgIB centered at 2θ = 64.42°.
It showed an rCl{420} diffraction peak. (corresponding to a composition of 35.6 mol% I, 32.2 mol% Br and 32.2 mol% Cl).

Example 6 This example shows AgBrC containing the main phase of rock salt type crystal structure and only a small amount of silver iodide phase with a composition of 30.2 mol % Br, 30.2 mol % Cl and 39.6 mol % I.
The preparation of the II emulsion is shown.

27.5 mol% Cl, 27.5 mol% Br
A fine-grain emulsion containing multiple phases with a combined composition of I and 45.0 mol % I was prepared by the following procedure. 150 mL/min into a stirred reaction vessel containing 4 L of 10% bone gelatin solution in 0.028 M NaCl at 40°.
and 1.16 M NaCl, 1 at the rate necessary to maintain pAg 7.5.
．． A 10M NaBr and 1.80M NaI solution was added.

A part of this fine grain emulsion was placed in an autoclave and heated to 689.5 kPa (100
psi). Add this to 160 ml while stirring.
The mixture was heated to 0.degree. C., maintained at this temperature for 5 minutes, and then cooled to 40.degree. C. over 3 minutes.

The emulsion obtained was composed of grains having an average diameter of 0.7 μm. The X-ray powder diffraction pattern of this emulsion showed that it was composed of a mixed halide phase with a rock salt type crystal structure and only a small amount of silver iodide. This mixed halide phase has a 2θ=64.
It showed reflection at 170° (full width at half maximum 0.32°). Since silver chloride and silver bromide are confined in the mixed halide phase, the reflection angle is 30.2
mol% Cl, 30.2 mol% Br and 39.6 mol%
It was shown that it consists of I.

[0058]

Effects of the Invention The silver halide grains exhibit a cubic lattice structure known to be useful in photographic applications, the chloride ion concentration is at least equal to or in excess of the bromide ion concentration, and the silver halide grains have a conventional cubic lattice structure. We have shown that it is possible to prepare silver halide emulsions containing higher levels of iodide than what has been achieved in the structure. Thus, the present invention improves the known advantages of iodide incorporated silver halide emulsions with grains of unique halide content, while retaining the known advantages of those containing chloride ions. Emulsions are now within the reach of those skilled in the art.

[0059]

[Brief explanation of drawings]

FIG. 1 illustrates in a matrix graph all possible selections of chloride, bromide and iodine ions or combinations that meet the total halide requirement.

FIG. 2 is a plot of relative intensity of X-ray diffraction versus scattering angle.

FIG. 3 is a photograph in place of a scanning electron micrograph of grains in an emulsion of the invention.

Claims (2)

[Claims] 1. A photograph comprising a high chloride silver iodohalide grain structure in which the proportions of chloride, bromide and iodide ions lie within the boundaries bounded by A, B, C and D in FIG. Silver halide emulsion. 2. Claim 1 comprising an iodochloride grain structure containing 13 to 50 mole % chloride based on total silver.
Photographic silver halide emulsion as described.